This application relates generally to fiber-optic communications. This application relates more specifically to optical wavelength cross-connect architectures used in fiber-optics applications.
The Internet and data communications are causing an explosion in the global demand for bandwidth. Fiber optic telecommunications systems are currently deploying a relatively new technology called dense wavelength division multiplexing (DWDM) to expand the capacity of new and existing optical fiber systems to help satisfy this demand. In DWDM, multiple wavelengths of light simultaneously transport information through a single optical fiber. Each wavelength operates as an individual channel carrying a stream of data. The carrying capacity of a fiber is multiplied by the number of DWDM channels used. Today DWDM systems employing up to 80 channels are available from multiple manufacturers, with more promised in the future.
In all telecommunication networks, there is the need to connect individual channels (or circuits) to individual destination points, such as an end customer or to another network. Systems that perform these functions are called cross-connects. Additionally, there is the need to add or drop particular channels at an intermediate point. Systems that perform these functions are called add-drop multiplexers (ADMs). All of these networking functions are currently performed by electronicsxe2x80x94typically an electronic SONET/SDH system. However, multi-wavelength systems generally require multiple SONET/SDH systems operating in parallel to process the many optical channels. This makes it difficult and expensive to scale DWDM networks using SONET/SDH technology. The alternative is an all-optical network. Optical networks designed to operate at the wavelength level are commonly called xe2x80x9cwavelength routing networksxe2x80x9d or xe2x80x9coptical transport networksxe2x80x9d (OTN). In a wavelength routing network, the individual wavelengths in a DWDM fiber must be manageable.
Optical wavelength cross connects are configured generally to redirect the individual optical channels on a plurality of input optical fibers to a plurality of output optical fibers. Each incoming channel may be directed to any of the output optical fibers depending on a state of the cross connect. Thus, where there are P input fibers and Q output fibers, the optical wavelength cross connect between them may be considered to be a xe2x80x9cPNxc3x97QN optical switch.xe2x80x9d Sometimes herein, the terminology xe2x80x9cPxc3x97Q optical wavelength cross connectxe2x80x9d is used to refer to such a cross connect by referring to the numbers of input and output optical fibers, each of which is understood to have the capacity for carrying N channels. As such the xe2x80x9cPxc3x97Q optical wavelength cross connectxe2x80x9d terminology may be considered to be a shorthand for describing a arbitrarily configurable PNxc3x97QN optical device.
FIG. 1 provides an example of a prior-art 4xc3x974 optical wavelength cross connect 100 for a DWDM system carrying N individual wavelength channels. Each of the N channels on the four input signals 104 may be redistributed in accordance with a state of the cross connect 100 among the four output signals 116. The cross connect 100 functions by splitting each of the input signals 104(i) with an optical demultiplexer 108(i) into N signals 120(1 . . . N, i) that carry only a single wavelength channel xcex1 . . . N. From each of the optical demultiplexers 108, the signal corresponding to a particular one of the 120(j, 1 . . . 4) is directed to a respective one of N4xc3x974 optical space switches 110(j). Each optical space switch 110 may be configured as desired to redirect the four received signals 120 to four transmitted signals 124. The transmitted signals 124 are transmitted to optical multiplexers 112 that recombine the reordered individual-wavelength signals onto the four output signals 116.
The efficiency of an arrangement such as shown in FIG. 1 is limited because it adopts a brute-force-type approach of demultiplexing the four incoming signals into their individual 4N components in order to reroute them. There is a general need in the art for more efficient optical wavelength cross-connect architectures without compromising complete routing flexibility.
In embodiments of the invention this routing flexibility is manifested with an ability to upgrade a Ki1xc3x97Kj1 optical wavelength cross connect to a Ki2xc3x97Kj2 optical wavelength cross connect without taking the cross connect out of service. Each of such Kixc3x97Kj cross connects comprises a working fabric having a plurality of optical components and a protection fabric. The working fabric is configured to receive optical traffic from Ki input optical signals and to transmit Kj output optical signals. The protection fabric is configured to bypass at least one of the optical components in the event of a fault. The upgrade of the Ki1xc3x97Kj1 optical wavelength cross connect proceeds by upgrading the protection fabric to accommodate at least Ki2 input optical signals. Sequentially, each of the optical components included on the working fabric is upgraded. The optical traffic received by that optical component is bypassed to the protection fabric. Thereafter, that optical component is upgraded to accommodate at least Ki2 input optical signals. Thereafter, the bypassed optical traffic is returned to that optical component. The upgrade of the protection fabric may generally be performed at any stage in the method with respect to upgrades of the working fabric. For example, it may be performed before any of the optical components on the working fabric are upgraded, it may be performed after all of the optical components on the working fabric have been upgraded, or may be performed at an intermediate time.
In one embodiment, upgrading the protection fabric includes increasing the capacity of the protection fabric so that a greater number of the optical components on the working fabric may be bypassed simultaneously. If the protection fabric in the Ki1xc3x97Kj1 optical wavelength cross connect is already capable of bypassing traffic from at least two of the optical components on the working fabric, a fault during the upgrade may be accommodated by bypassing additional traffic to the protection fabric in response.
In certain embodiments, the optical components on the working and/or protection fabric comprise wavelength routing elements. A wavelength routing element is adapted generally for selectively routing wavelength components between a first optical signal and a plurality of second optical signals according to a configurable state of the wavelength routing element. In some embodiments, at least one wavelength routing element comprised by the optical wavelength cross connect may be a four-pass wavelength routing element; in other embodiments, it may be a two-pass wavelength routing element.
In further embodiments, the Ki1xc3x97Kj1 optical wavelength cross connect also comprises a plurality of optical splitters configured to direct an equivalent to each of the input optical signals either to at least one of the optical components included on the working fabric or to the protection fabric. In such embodiments, the method may further comprise increasing a splitting capacity of each of the optical splitters. In one such embodiment, each of the optical splitters is configured to direct equivalents to all of the optical components included on the working fabric. Increasing the splitting capacity of each of the optical splitters may comprise adding a further optical splitter to each output of the optical splitters that corresponds to a bypassed optical component while that optical component is bypassed.